Centrifuge equipment may be used to separate a biological or chemical sample into sample components based upon differences in molecular weight. The availability of a variety of types of centrifuge rotors increases the versatility of the equipment in biological and chemical experimental research. For a selected separation process, a rotor model is selected according to the sample of interest and the physical characteristics of the rotor.
The centrifuge must be adapted to interchangeably mount any of a variety of models of rotors onto a rotational drive shaft. Conventionally, a centrifuge rotor is connected to the drive system by a metal hub. The hub is fixed to a drive shaft of the drive system and is releasably coupled to the rotor to transmit torque power from the drive shaft to the rotor. The hub may have one or more prongs that project upwardly in parallel relationship with the drive shaft from the top of the hub. Each rotor includes structure for mating with the prongs of the hub. Typically, the rotor slides onto the hub.
A difficulty that has been encountered is that while a rotor will freely slide onto a hub, the rotor becomes fastened to the hub following the centrifuge process. As the rotor is spun, the physical characteristics of one or both of the hub and the rotor change, so that the hub becomes locked to the rotor. One possible explanation for this phenomenon is that the centrifugal force causes the rotor to expand to a greater degree than the hub. A rotor may be aluminum, while the hub is formed of stainless steel. Often, the rotor is supported on a sloped surface of the hub. The theory is that the differential in expansions allows the rotor to descend as the assembly is spun. Then, when the rotor is brought to rest, the rotor and the hub return to their original dimensions. However, the geometries of the hub and the rotor are such that the rotor does not ascend to the original position relative to the hub. As a result, the rotor clamps onto the hub.
Because the fastening members for connecting the hub to the drive shaft are typically not accessible when a rotor is supported on the hub, rotor-to-hub lock may result in the need to replace an entire centrifuge drive system. At the least, the rotor must be discarded if the rotor cannot be detached from the hub. Thus, there is a substantial cost involved. As centrifuge systems increase in their capability to rotate biological and chemical samples at higher speeds, the potential of rotor-to-hub lock increases.
Attempts have been made to coat the hub with the synthetic resin polymer sold by E. I. DuPont Company under the trademark TEFLON. However, the coating is susceptible to scratches and deterioration. Replacement of the coating is expensive.
It is an object of the present invention to provide an assembly for releasably connecting a centrifuge rotor to a centrifuge drive system, with decreased susceptibility to rotor-to-drive lock.